1. Field of the Invention
The present invention relates to color balance, more particularly, white balance in a digital camera (electronic camera).
2. Description of Related Art
As for the prior art concerning white balance, a method of white balance has been proposed in Jpn. Pat. Appln. KOKAI Publication No. 5-7369. Conventionally, for a video camera or still camera, the control processing of white balance has been performed assuming that an “achromatic color (for example, gray) can be obtained by averaging the whole image”. However, a problem occurs that the color reproducibility of an object illuminated with a fluorescent lamp can not be improved totally by such processing. The following solutions have been proposed to solve this problem. Namely, it is determined whether a camera is located outdoors or indoors, according to a brightness higher or lower that a predetermined brightness (Y), and if it is indoors, the kind of light source is identified according to a value of a white balance control signal (R CONT, B CONT) that would make a value of a color-difference signal (R−Y, B−Y) equal to a reference value. Then, the color reproducibility is improved through modification of magnification of a primary red signal R and a primary blue signal B, by limiting the magnification of these primary red signal R and primary blue signal B, according to the identified kind of light source. Therefore, the countermeasure as mentioned above permits preventing inconveniences due to excessive correction, for example, discoloration of the background, or excessive correction of colors of the main object.
Moreover, there is a white balance control method as taught in Jpn. Pat. Appln. KOKAI Publication No. 9-90459. Here is proposed to discriminate artificial light/natural light based on the balance of visible light photometric value and infrared light photometric value (in short, ratio of visible light component and infrared light) and to emit light from an electric flash device according to the ratio of the visible light component and infrared light, as processing for correction (mixed light correction) of color balance on a photographic print due to the color mixture by a fluorescent lamp or electric lamp.
It has been possible to correct the color balance, and improve somewhat the color reproducibility by using such prior art.
However, in said Jpn. Pat. Appln. KOKAI Publication No. 5-7369, though the kind of light source is determined according to the value of the white balance control signals R CONT and B CONT that would make the value of the color-difference signals R-Y and B-Y equal to a reference value, after all, it is determined by the ratio of values of R, B and Y, the kind of light source might be determined inaccurately and the correction becomes insufficient or excessive according to the actual color of the object.
On the other hand, in said Jpn. Pat. Appln. KOKAI Publication No. 9-90459, though the kind of light source is determined based on the visible light photometric value and the infrared light photometric value, the color is simply improved by emitting light from an electric flash device when the light source is determined to be artificial, and there is no reference to the digital color signals R, G and B. Besides, in case of this conventional example, as a result of determination of the light source kind, there is nothing but a straight choice between emitting/non-emitting the electric flash device, and there is no other option than emitting/non-emitting even in the case of a slight color mixture as, for example, by a window under a fluorescent lamp, and a further fine correction appropriate for such a situation is impossible. Therefore, a camera that can correct “color mixture” even at a window side under an artificial light source is required.
It is an object of the present invention to provide a camera, such as a digital camera, capable of white balance correction that would correct the color mixture of an artificial light from a light source, in the case where the light source is determined to be artificial based on a visible light photometric value and an infrared light photometric value.